Short Message Service (SMS) is a service in Global System for Mobile Communications (GSM)/Universal Mobile Telecommunications System (UMTS) which does not require creating end-to-end service paths. A mobile station is able to transmit short messages under all-circuit communication situation. Generally, a short message communication involves only one message. That is, a transmission of one message represents one communication. Therefore, the SMS is an asymmetric service including a Short Message-Mobile Originated (SM-MO) transmission and a Short Message-Mobile Terminated (SM-MT) transmission. The transmission of the short message relies on a Short Message Service Center (SMSC) external to the GSM/UMTS relaying the message.
FIG. 1 illustrates a conventional system architecture for transmitting short messages where the system supports Internet Protocol (IP). This system architecture is directed to implement SMS by employing a protocol supported by user equipment (UE). For instance, the system may be an IP Multimedia Subsystem (IMS). In this architecture, IP Short Message Gateway (IP-SM-GW) may interact with existing elements such as Gateway Mobile Switching Center For Short Message Service (SMS-GMSC)/Interworking Mobile Switching Center For Short Message Service (SMS-IWMSC), SMSC, Home Location Register/Home Subscriber Server (HLR/HSS). With the improvement of the capability of the mobile station, mobile station, especially IMS based Session Initiation Protocol (SIP) terminal, is able to receive and transmit short messages in various formats. For instance, the mobile station may be able to receive and transmit textual, audio, animated or graphical short messages. Generally, the lengths of these short messages are long. In order to be compatible with the existing short messaging system, IP-SM-GW may split or combine these short messages.
FIG. 2 illustrates a conventional architecture of on-line charging for short messages. In this architecture, before the user who has pre-paid the fee for the short messages sends or receives a short message, the SMSC is responsible for interacting with an Online Charging System (OCS) or an intelligent network system so as to handle the authentication request from the user who has pre-paid the fee and handle the fee deduction operation. However, the conventional online charging for short message has the following disadvantages. When the user uses an IMS based terminal to send a short message, since a Session Initiation Protocol (SIP) message is able to carry a considerable length of content for the short message, the IP-SM-GW may convert the SIP message carrying short message content with a considerable length into multiple normal short messages in accordance with the restriction on the length of normal short message. However, according to the existing charging scheme, the charging system will charge the converted multiple short messages by different charging standards. Apparently, this is unfair to the user and thus the user is less satisfied.